Implement scheduleTask in TestWakeupClientService.

Handles the schedule task request from GRPC. Starts a thread
for the scheduled tasks and injects the task data through the grpc
channel.

Test: m -j TestWakeupClientServerHost && atest TestWakeupClientServerHostUnitTest
Bug: 297271235
Change-Id: Ia9f1d7fa3dadb3be68e31987622bc6df9271e929